There are hundreds of ways to brew coffee and, for the most part, they all produce coffee that tastes like you'd expect coffee to taste. So, in the past, I've never worried much about how to brew the coffee, just that I wanted my coffee to be good, hot and full of caffeine. That all changed a few years ago when I really started to explore the chemistry of coffee - from roasting coffee to brewing coffee and I became fascinated with finding ways to make coffee taste amazing. In fact, every year in my High School Chemistry class, we do a 10 day lab called the Chemistry of Coffee to intertwine the key concepts of chemistry into roasting, brewing and perfecting the art and science of coffee.
I recently watched a cup of coffee being brewed with a siphon brewer (vacuum brewer) and was completely mesmerized at how beautiful this brewing process looked and, in the end, how incredible it tasted. So, I purchased a siphon brewer and it rocked my world as much as it rocked my bank account. I began to think that I should be able to make a similar device using chemistry equipment and, alas, that is what I did. This page holds all of the information, instructions and equipment needed to build a siphon brewer at home; or, as in my case, in the science lab.
How to build a siphon brewer from lab equipment
Supplies (all links redirect to Amazon.com)
Setting up the Homemade Siphon Brewer
-Watch the video "Brew Perfect Coffee with Chemistry Equipment" for complete instructions in building and setting up the siphon brewer.
How to brew coffee in the homemade siphon brewer
Note: The amount of water and coffee grounds will vary depending on the size of your glassware
Wrap the end of the funnel with a coffee filter. Secure in place by tightly wrapping with cotton string. Note: Rubber bands may be used but we've had better success with tightly wrapped string.
Fill Florence Flask with hot water. Keep track of how much water so you know how many coffee grounds to use (see step 7 below) Note: You can start with room temperature water but the process will take much longer
Light the burner and place it under the Florence Flask.
Insert glass tube with rubber stopper into Florence Flask. Do not insert the stopper all the way, you want to allow the flask to vent until you've set up the rest of the apparatus.
Insert the funnel with coffee filter into the beaker and move the iron ring so the filter is nearly touching the bottom on the flask (leave a 1 mm gap).
Firmly push the rubber stopper into the Florence Flask.
Once water starts to move into the beaker with the filter, add coffee . For perfect coffee, use your favorite roast, ground to medium and no less than 1 heaping tablespoon per 6 oz of water that you placed in the Florence Flask.
When all of the water has moved into the beaker with coffee grounds, set a timer for 1.5 minutes and turn down the burner slightly. You must keep the Flask hot enough that liquid will not flow back into the flask.
After 1.5 minutes, remove the burner from the bottom of the Florence Flask - the coffee should be pulled from the beaker and coffee grounds, back into the Flask.
Drink. Enjoy. Repeat.
How Does a Siphon Brewer Work? The Science of Brewing with a Siphon Coffee Pot
The vacuum brewer is a perfect way to model and learn about gas laws and, while the brewing apparatus is relatively simple, the chemistry and physics of how it works is surprisingly complex. I will "boil" the complexity of down to its simplest form:
There are numerous gas laws that help explain how temperature, pressure and volume of gases are related in a closed and open system such as our homemade coffee siphon brewer. These gas laws can be combined into one equation - the Ideal Gas Law:
P= Pressure of the gas (pascals)
V= Volume of the gas (cubic meters)
n= number of moles (amount of "substance")
R= ideal gas constant (8.318 J/K*mol)
T= Temperature of the gas (Kelvin)
For an extensive explanation of how the siphon brewer works using the ideal gas law, click "The Physics of Vacuum Pots". A simplified explanation, with out the math, is below.
The physics of the Siphon Coffee Brewer
Start of brewing: With water heating in the Florence flask, the water begins to turn to a vapor, increasing the pressure in the flask above the water. This increased pressure pushes in all directions, including putting pressure on the water. The pressure inside the glass tube and in the beaker on the opposite end of the tube is much less than the pressure in the round flask at this point. This difference in pressure causes the liquid to be pushed into the glass tube flow toward the lower pressure end.
Middle of Brewing: Once all of the water has moved from the round flask into the beaker and the coffee is brewing, the continued heat in the round flask keeps the increased pressure in the flask, causing the brewing coffee to remain in the beaker.
End of Brewing: Removing the heat from the round flask decreases the temperature of the gas (water vapor) in the flask and it begins to condense into water droplets. Water takes up less space (less volume) than a gas so the volume begins to decrease in the flask (although it is a closed system so the volume cannot decrease) which causes the pressure to drop. Once the pressure in the round flask is less than the pressure at the other end of the tube, the brewed coffee is pushed through the filter, into the tube and back into the round flask. This process is called siphoning or vacuuming and is how this method gets it's name "Siphon Coffee" or "Vacuum Coffee"!
For instructions, lessons and videos on the Science of Coffee and the Chemistry of Coffee, visit BealsScience.com/Coffee-Science
Happy Coffee Brewing! ~Craig